This project involves FDG-PET scanning of patients who have brain tumors before and during deep barbiturate general anesthesia. The results indicate that a profound reduction of cerebral glycolytic activity can be achieved with a level of anesthesia which produces burst-suppression EEG activity. Gliomas, however, have only a minimal change in glycolytic rate under the barbiturate anesthesia. The results also indicate that lower grade lesions, which are to visible on PET scans performed with the patient awake, become visible as background synaptic activity is suppressed with barbiturates. The true extent of growth into the surrounding tissue by higher grade lesions can be better appreciated when background activity is reduced under the barbiturate anesthesia. Since coma producing doses of barbiturates would be inconvenient for clinical use, we investigated the possibility of achieving a portion of this effect using sedative doses of pentobarbital. This resulted in the demonstration that about 50% of the suppression of glucose metabolism by normal brain using coma-producing doses of barbiturates can be achieved by pre-anesthetic (sedative) doses of pentobarbital. Therefore, using doses of pentobarbital that could be used repeatedly and conveniently in the clinic, we have achieved suppression of brain metabolism while leaving tumor metabolism unaffected. This work provides evidence that barbiturates may allow a "reverse contrast enhancement" of lesions with decreased neuronal activity. This phenomenon may provide a basis for development of specific antitumor therapy. The technique also may be valuable in studying other pathological processes such as degenerative diseases, epilepsy, movement disorders, cerebral infarction and head injury.